1. Field of the Invention
The present invention relates to a discharge device which causes a change of a capacity of a pressurizing chamber by use of a strain induced by an electric field to discharge a fluid from the pressurizing chamber.
2. Description of the Related Art
In recent years, in apparatuses which perform printing such as a printer, a facsimile machine and a photocopier, most of printing systems have been performed by a non-impact laser or an ink jet head. Especially, in a small printer, a high-performance ink jet head is frequently used, and anyone can readily reproduce a clear image on paper as in a silver salt photograph as well known. The ink jet head mainly includes a piezoelectric system and a thermal jet (Bubble Jet (registered trademark) or the like) system in accordance with a difference of a mechanism which discharges ink. Among the systems, the ink jet head of the piezoelectric system is an ink jet head in which a piezoelectric element is used as a driving source, and the head mainly includes a nozzle, an ink chamber which communicates with an ink supply path and a piezoelectric element which changes a capacity of the ink chamber. In a printer (an ink jet printer) in which the ink jet head of the piezoelectric system is adopted, a driving voltage is applied to the piezoelectric element to change the capacity of the ink chamber in accordance with displacement of the element, and the ink is discharged from the nozzle of the ink chamber to thereby perform the printing. In the ink jet head of this piezoelectric system, unlike the thermal jet system, the ink is not heated. Therefore, the head advantageously has a high degree of freedom in selection of the ink, and an excellent controllability.
In such an ink jet head of the piezoelectric system, mainly improvements are demanded in order to realize denser printing at a higher speed and to achieve a broad range of properties of the ink to be handled, and to use a highly viscous liquid (ink) or a solvent-based liquid (ink) in which an organic solvent is used as a solvent.
(1) First, further improvements of arrangement densities of the piezoelectric elements and the ink chambers and further improvement of an ink discharge force are required. The further improvements of the arrangement densities are positioned as basic technical problems directly related to the realization of the dense printing at the high speed. The further improvement of the ink discharge force is a problem to be achieved in order to realize the discharging of a broad range of liquid (ink) such as pigment-containing ink or highly viscous ink.
(2) Next, inhibition of generation of crosstalk is required. When the piezoelectric elements are highly densely arranged, mutual interference (i.e., the crosstalk) is easily caused owing to displacements between the piezoelectric elements arranged adjacent to each other. This might deteriorate the ink discharge force or cause fluctuations in a discharge direction of the ink. Therefore, it could be an important problem to prevent the crosstalk from being easily caused.
(3) Furthermore, since the piezoelectric elements and the ink chambers are highly densely arranged, manufacturing steps might become complicated, and positions of the piezoelectric elements and the ink chambers might deviate to deteriorate yield. Therefore, a manufacturing method for avoiding these problems and a structure which is precisely and easily manufactured are important technical themes.
It is to be noted that to meet such improvement requirements, proposals have heretofore been made. Examples of prior art documents include Patent Documents 1 to 6:
[Patent Document 1] Japanese Patent No. 3298755;
[Patent Document 2] Japanese Patent Application Laid-Open No. 2004-358716;
[Patent Document 3] Japanese Patent No. 3227285;
[Patent Document 4] Japanese Patent Application Laid-Open No. 2005-19971;
[Patent Document 5] Japanese Patent No. 3231523; and
[Patent Document 6] Japanese Patent No. 3480481.
However, it has been considered that conventional technologies proposed in the prior art documents have problems, respectively. In an ink jet head disclosed in Patent Document 1, from the above viewpoint (2), piezoelectric elements to be actually driven for use in pressurizing ink chambers are arranged alternately with fixed piezoelectric elements which are not driven (see FIG. 4 of Patent Document 2). This configuration is adopted to inhibit generation of crosstalk. Therefore, it can be said that nozzles can be arranged as ink discharge ports at pitches which are only halves of those of the piezoelectric elements formed by mechanical processing (slit processing). Therefore, there is a limitation from the above viewpoint (1) which is a basic problem. An ink jet head disclosed in Patent Document 2 also has a similar problem.
In an ink jet head disclosed in Patent Document 3 and a cell driving type piezoelectric/electrostrictive actuator or micro pump according to Patent Document 4 proposed beforehand by the present applicant, there is not any piezoelectric element that is not driven. However, from the above viewpoint (2), an ink chamber is formed by two piezoelectric elements which are not shared by another ink chamber. This configuration is adopted to inhibit generation of crosstalk. Therefore, one nozzle is disposed for two piezoelectric elements. The nozzle can only be disposed at a pitch which is a half of that of the piezoelectric element in the same manner as in the ink jet head disclosed in Patent Document 1. Therefore, this structure is not necessarily preferable from the above viewpoint (1) which is the basic problem.
In Patent Document 5, there is proposed an on-demand type ink jet head including an actuator unit constituted by arranging, in one row, piezoelectric elements constituted by laminating a plurality of sets of piezoelectric materials and electrode materials; a plurality of rows of liquid chamber units with respect to the actuator unit; and nozzle units connected to the liquid chamber units. In this on-demand type ink jet head, a one-to-one correspondence exists between the piezoelectric element and the liquid chamber (the ink chamber), and high integration is easily achieved. It can be said that the head is preferable from the above viewpoint (1). Even when the high integration is achieved, there is not restriction on a shape of the liquid chamber. Therefore, it is possible to realize a high ink discharge efficiency. In this on-demand type ink jet head of Patent Document 5, however, a frame is disposed around the piezoelectric elements arranged in the actuator unit. In this frame portion, the actuator unit is integrally bonded to the liquid chamber unit including the ink liquid chambers. It is considered that rigidity is secured by such a structure and that the crosstalk is not easily caused (the above viewpoint (2)). Therefore, even when the piezoelectric elements and the liquid chambers can highly be integrated, the whole ink jet head enlarges. Moreover, separate units need to be bonded. In consideration of strengths required for the bonding, securement of position precisions of the units during the bonding and the like, from the above viewpoint (3), it can be said that the head has a large number of worries and that the head is not necessarily preferable. When a position of the piezoelectric element deviates from that of the liquid chamber (unit), a size and a configuration (a deformed shape) of deformation of a partition wall member in a vibration plate region change, fluctuations are generated in displacement of the liquid chamber, and high-quality printing cannot be performed.
Even in an ink jet head type recording head disclosed in Patent Document 6, a one-to-one correspondence is established between a piezoelectric vibrator (a piezoelectric element) and a pressure generation chamber (an ink chamber). In this respect, it can be said that the head has a preferable configuration from the above viewpoint (1). However, in this ink jet head type recording head, it is considered that the piezoelectric vibrator is inserted into a frame, and fixed to the frame via a fixed substrate to secure rigidity and inhibit generation of crosstalk (the above viewpoint (2)). The frame made of plastic or the like which is easily processed is adopted. Therefore, to secure strength of a structure, the frame remarkably enlarges as compared with sizes of the piezoelectric vibrator and the pressure generation chamber (see FIGS. 1 and 2 of Patent Document 6). To solve a problem of a coefficient of thermal expansion caused by the adoption of the frame made of plastic or the like, manufacturing requires a step of injecting an adhesive in a groove of the frame or the like. Therefore, even if the piezoelectric vibrators (the piezoelectric elements) and the pressure generation chambers (the ink chambers) can highly be integrated, the whole ink jet type recording head cannot be miniaturized. In consideration of manufacturing steps or the like, the head is not necessarily preferable from the above viewpoint (3). Since a distal end of the piezoelectric vibrator is not grasped, a position of the piezoelectric vibrator easily deviates from that of the pressure generation chamber. Therefore, fluctuations of displacement of the pressure generation chamber might be generated, and high-quality printing would not be realized.